Hydrodimerization process of acrylic compounds

ABSTRACT

THE HYDRODIMERIZATION OF ACRYLIC COMPOUNDS IS MATERIALLY IMPROVED BY EFFECTING SAME IN THE PRESENCE OF AN ALKALI OR ALKALINE EARTH METAL AMALGAM IN A MEDIUM OF LIQUID CONSISTENCY CONTAINING THE ACRYLIC COMPOUND(S), FROM 0.1 TO 100 MILLIEQUIVALENTS OF ACID PER LITER AND AT LEAST ONE NON-REACTIVE AMIDE.

nited States Patent 5 Int. or. C07c 12i/26, 121/20, 121/16 U.S. Cl. 260-465.8 A 6 Claims ABSTRACT OF THE DISCLOSURE The hydrodimerization of acrylic compounds is materially improved by efi'ecting same in the presence of an alkali or alkaline earth metal amalgam in a medium of liquid consistency containing the acrylic compound(s), from 0.1 to 100 milliequivalents of acid per liter and at least one non-reactive amide.

The present invention is related to a new process for the hydrodimerization of acrylic compounds, more particularly to the production of adiponitrile from acrylonitrile.

There are several types of processes for the hydrodimerization of acrylonitrile to adiponitrile, either by direct electrolysis or by the use of an amalgam of a reducing metal, a finely divided reducing metal or an organometallic complex. The process of the present invention belongs to the second of these categories.

A process for the hydrodimerization of acrylonitrile using sodium amalgam was reported in 1949 (O. Bayer, Angew. Chem. 81, (1949), 238). However, the yield of adiponitrile, based on the amount of acrylonitrile used, was only 5%. Magnesium amalgam in presence of a methanolic solution has also been proposed (US. patent specification No. 2,439,308) but the adiponitrile yield, based on the acrylonitrile used, is also inignificant. More recently (Knunyants and Vyazankin, Doklady Akad. Nauk SSR, 113, (1957), 112-115) this yield has been brought up to more than 60% by treating a 20% solution of acrylonitrile in hydrochloric acid with potassium amalgam.

Since then, other suggestions have been made to improve Knunyants method (loc. cit), namely, the use of at least 0.5 mol of alkali metal or alkaline earth metal per mol of acrylonitrile (Canadian patent specification No. 649,789, the yield being at least 85%, based on the amount of acrylonitrile consumed), the use of a polymerization inhibitor of a salt of a transition metal and of acetone (French patent specification No. 1,289,071, the yield reaching as much as 75% based on the acrylonitrile used), and the addition of various metallic salts to increase the adiponitrile/propionitrile ratio (Belgian patent specification No. 644,877).

There is, however, no reference in any of the publications mentioned above to a yield of adiponitrile based on the amount of alkali metal or alkaline earth metal consumed.

Now, the hydrodimerization of acrylonitrile in an acid aqueous medium gives rise to important secondary reactions, especially the liberation of hydrogen by the reaction of the reducing metal with the acid present in the reaction medium and the reduction of acrylonitrile to propionitrile.

In the processes described in the publications mentioned above, the first of these reactions is so important that, under the most favorable reaction conditions, a maximum of 30% of the reducing metal employed is used in the actual hydrodimerization of acrylonitrile to adiponitrile, i.e. more than 70% of it is consumed to form hydrogen.

'As the alkali metal or alkaline earth metal amalgam is produced by electrolysis, the cost of the electric power required must be taken into account as well as the increase in investment necessary to cover the low yield based on reducing metal. Thus, in the process mentioned, the adiponitrile yield, based on the amount of electric power consumed in preparing the amalgam, is at most 30%. In the description which follows, the expression power efiiciency is used to represent this concept.

The second of the secondary reactions mentioned above, namely, the reduction of acrylonitrile to propionitrile, is also of importance. Indeed, since adiponitrile is the desired product, operational conditions have to be sought which will provide as high an adiponitrile/propionitrile ratio as possible.

As will be seen below, the process of the present invention improves the power efliciency of the acrylonitrile hydrodimerization to adiponitrile and, at the same time, gives excellent yields of adiponitrile based on acrylonitrile as well as a high adiponitrile/propionitrile ratio.

According to the present invention, the process of hydrodimerization of acrylic compounds by the action of an alkali or alkaline earth metal amalgam in the presence of an organic or inorganic acid is characterized by the fact that it is carried out using a reaction medium of liquid consistency containing the acrylic compound, at least one amide and optionally water, the acid concentration being low enough to avoid the formation of hydrogen and to limit that of the hydrogenated product of said acrylic compound.

By acrylic compound is to be understood acrylonitrile, methacrylonitrile, acrylic and methacrylic esters, acrylamide and methacrylamide as Well as their mixtures.

By reason of the commercial importance of adiponitrile, the present invention is described while referring more particularly to the hydrodimerization of acrylonitrile to adiponitrile, but it is to be understood that the process has a wider scope as is more specifically shown by the Examples 12 to 16 hereafter.

Thus, according to one of its aspects, the present invention is related to a process of hydrodimerization of acrylonitrile to adiponitrile by the action of an amalgam of an alkali metal or alkaline earth metal in the presence of an inorganic or organic acid characterized by the fact that it is carried out using a reaction medium of liquid consistency containing acrylonitrile, at least one amide and optionally water, the acid concentration being low enough to avoid the formation of hydrogen and to limit that of propionitrile.

Applying the methods proposed by the present invention, the adiponitrile yield, based on the amount of acrylonitrile consumed, is at least 65% and may reach more than while the adiponitrile yield in relation to the amount of alkali metal or alkaline earth metal consumed (power efliciency) is at least 60% and may exceed 90%. The amount of metal consumed in the formation of gaseous hydrogen is always less than 10% and often nil. As far as is known, such power efficiencies have not been previously attained in hydrodimerization processes where the source of adiponitrile is exclusively acrylonitrile, which indicates the technical advance and economic interest of the process of the present invention. Furthermore, the adiponitrile/propionitrile ratio is very favorable and lies between 20/1 and 50/1 and may even reach and exceed /1.

In the following description, reaction mixture or mixture means the reaction medium, excluding the alkali metal or alkaline earth metal amalgam.

By alkali metal or alkaline earth metal amalgam, there is meant a mercury amalgam of a metal of Groups Ia and 11a of the Periodic System, the preferred metal being potassium. The concentration of alkali metal or alkaline earth metal in the amalgam is not critical and may range from 0.01 to 0.5% by weight but it is, in principle, possible to work outside these limits. However, below a concentration of 0.01%, extremely large quantities of mercury have to be used, while it is at present difficult to produce industrially amalgams containing more than 0.5% by weight of amalgamated metal.

The molar potassium/acrylonitrile ratio is determined by the desired acrylonitrile conversion rate. Since the formation of propionitrile requires, per mole of converted acrylonitrile, twice as much potassium as that of adiponitrile, it may be necessary, for high conversions, for example of the order of 90% and over and in cases where the formation of a small quantity of ropionitrile is accepted, to use a molar potassium/acrylonitrile ratio of efficiency, it is desirable not to exceed a ratio of 1.5 and more than one. However, in order to maintain good power preferably not even 1.1.

According to the present invention, at least one amide is used so that, under the reaction conditions, the reaction mixture is of liquid consistency. It is preferable to use amides of carboxylic acids, which may be unsubstituted or substituted on the nitrogen, for example, formamide, N,N- dimethyl formamide, acetamide, N,N-dimethyl-acetamide, propionamide and the like. Sulfonamides, such as p-toluene-sulfonamide and amides of inorganic acids, for example, hexamethyl phosphoramide and the like, may also be used. The preferred amide is formamide, a product of low cost which is readily available. The amount of amide used represents, by weight, 10 to 95%, preferably 20 to 90%, of the reaction mixture. Instead of one amide, a mixture of two or more amides may be used. The solubility of the amides in the mixture may be improved by the addition of auxiliary solvents, such as dioxane.

The inorganic or organic acid may be used either pure or in solution. The quantity used is frequently stoichiometrically equivalent to the quantity of alkali metal or alkaline earth metal consumed in the reaction. However, in order to avoid the liberation of hydrogen, which would reduce the power efficiency, the acid concentration in the reaction mixture should be between 0.1 and 100 meq. (meq.:milliequivalent) per liter. When the acid content is less than 0.1 meq./liter, there is an increased risk of secondary reactions, such as polymerization of the acrylonitrile and various cyanoethylation reactions, whereas, when it exceeds the upper limit, the amount of hydrogen liberated becomes quite large.

In fact, when Working within the above-mentioned limits, only minor quantities of high boiling products (cyanoethylation and polymerization products) are formed. Furthermore, the amount of hydrogen liberated is less than 10% (in mols per equivalent of alkali metal or alkaline earth metal consumed) and is most often nil.

It is also possible to use an inorganic acid, such as hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, hydrofluoric acid, hydrobromic acid, and the like, or a monoor polycarboxylic organic acid, such as formic acid, acetic acid, propionic acid, oxalic acid, tartaric acid and the like.

The acrylonitrile concentration in the reaction mixture is between 1 and 80% by weight, preferably between 5 and 60% by weight. In the continuous process, the concentration of acrylonitrile may be kept as low as 5% during the whole course of the reaction.

A certain amount of water may be present in the reaction mixture, its concentration may vary from 0 to 50% by weight and is preferably between 0 and by weight.

The technical acrylonitrile used in the hydrodimerization reaction according to the present invention is a product containing a polymerization inhibitor to ensure its stability during storage. The amount of inhibitor added to the product is sufiicient to prevent the formation of polymers under the operational conditions. However, a further amount of polymerization inhibitor may be added to the acrylonitrile, for example, hydroquinone or its methyl ether, p-tert.-butyl-catechol, alpha-amino-anthraquinone, phenothiazine and the like. Such further amount of inhibitor may vary from 0.01 to 1% by weight, based on the acrylonitrile. The acrylonitrile used may be a commercial product, or it may contain acetonitrile as often does the product directly withdrawn from the purification cycle of an acrylonitrile synthesis from propylene, air and ammonia.

During the hydrodimerization of the acrylonitrile, the temperature is betwen 0 and 50 0., preferably between 10 and 30 C.

The process of the present invention may be carried out discontinuously, semi-continuously or entirely continu ously; it offers the advantage that the hydrodimerization products can be easily isolated and recovered by the usual methods, such as distillation and extraction.

The process of the present invention is not limited to any particular apparatus. Any apparatus may be used which maintains an intimate contact between the amalgam of the reducing metal and the reaction mixture.

In the following examples, the reactor used consists of a vertical tube filled with Raschig rings and surrounded by a sleeve serving for the thermostatic control of the reaction mixture, the latter being continuously recycled by a pump. The mercury amalgam is introduced into the top of the tube and dispensed in droplets, the used mercury running out through the bottom of the reactor. The filling may be eliminated if one of the reaction products precipitates in solid form during the reaction (e.g. potassium chloride, potassium sulfate or potassium acetate). The neutralizing acid is introduced into the circulating reaction mixture by means of a metering pump.

The acid concentration is checked by measurement of the difference of potential existing between a glass electrode immersed in the reaction medium and a saturated calomel electrode. The millivolts are converted into acid concentrations (milliequivalents of acid per liter of reaction mixture) by means of a calibration curve.

In the following examples, which are given for the purpose of illustrating the present invention, conversion means the proportion of reagent consumed in relation to the quantity used and yield means the proportion of product formed in relation to the reagent actually consumed. All parts and proportions are by weight unless otherwise indicated.

EXAMPLE 1 11.84 kg. potassium amalgam containing 17.08 g. potassium (0.144% potassium/amalgam) is passed through the above-described apparatus, which contains a solution consisting initially of 27.5 g. acrylonitrile (9.8% by weight), 5.5 g. acetic acid, 27.5 g. water, 0.275 g. hydroquinone and 220 g. formamide. The temperature is maintained at 20 C. At the same time as the amalgam, a stoichiometrically equivalent quantity of glacial acetic acid is added in such a manner that the acid concentration is maintained at 7 meq./liter during the reaction. The experiment last minutes. The results obtained are as follows:

Acrylonitrile conversion, percent 82.0 Potassium conversion, percent Adiponitrile yield in relation to acrylonitrile, percent 69.5

Adiponitrile yield in relation to potassium, percent 68.0 Propionitrile yield in relation to acrylonitrile, percent 12.4 Propionitrile yield in relation to potassium, percent 26.0 Adiponitrile/propionitrile weight ratio 5.5 Gaseous hydrogen produced, percent 2.05

EXAMPLE 2 In this example, the water content of the reaction mixture is reduced.

A solution initially containing 23.0 g. acrylonitrile Acrylonitrile conversion, percent 91 Potassium conversion, percent 100 Adiponitrile yield in relation to acrylonitrile, percent 76.0

Adiponitrile yield in relation to potassium, percent 60.2 Propionitrile yield in relation to acrylonitrile, percent 20.3 Propionitrile yield in relation to potassium, percent 32.0 Adiponitrile/propionitrile weight ratio 3.7 Gaseous hydrogen produced, percent 3.3

EXAMPLE 3 In this example, the experiment is performed in the absence of water and the proportion of acrylonitrile in the reaction mixture is increased.

The mixture treated initially contains 96.0 g. acrylonitrile (34.3% by weight), 5.5 g. glacial acetic acid and 179.0 g. formamide. No extra inhibitor is added. Hydrodimerization is effected with 12.34 kg. potassium amalgam containing 17.25 g. potassium (0.1395 potassium/ amalgam). As in the preceding examples, the temperature is maintained constant at 20 C. and a stoichiometrically equivalent quantity of glacial acetic acid is added at the same time as the amalgam so that the acid concentration of the mixture is maintained at 1 meq./liter. The experiment lasts 90 minutes. The following results are obtained:

Acrylonitrile conversion, percent 21.9 Potassium converion, percent 100 Adiponitrile yield in relation to acrylonitrile, percent 83 Adiponitrile yield in relation to potassium, percent 74.2 Propionitrile yield in relation to acrylonitrile, percent 8.3

Propionitrile yield in relation to potassium, percent 14.45 Adiponitrile/propionitrile Weight ratio Gaseous hydrogen, produced, percent 1.4

EXAMPLE 4 In this example, the acetic acid is replaced by gaseous hydrogen chloride (1.5 meq./liter). The quantities present initially are 27.5 g. acrylonitrile (10% by weight), 27.5 g. water and 220 g. formamide. No extra inhibitor 'is added. 12.15 kg. potassium amalgam containing 18.85 g. potassium (0.147% potassium/amalgam) is used. A stoichiometrically equivalent quantity of hydrogen chloride is added at the same time as the amalgam so that the acid concentration is maintained at 1.5 meq./liter. The working temperature is C. and the experiment lasts 90 minutes. The results obtained are as follows:

Acrylonitrile conversion, percent 85.0 Potassium conversion, percent 100 Adiponitrile yield in relation to acrylonitrile, percent 78.8 Adiponitrile yield in relation to potassium, percent 75.7 Propionitrile yield in relation to acrylonitrile, percent 11.55 Propionitrile yield in relation to potassium, percent 22.2 Adiponitrile/propionitrile weight ratio 6.7 Gaseous hydrogen produced Undetermined.

6 EXAMPLE 5 In this example, a higher proportion of acrylonitrile is used in the reaction mixture than in Example 3.

The mixture treated initially contains 199 g. acrylonitrile (73% by weight), 5.5 g. glacial acetic acid, 68 g.

'formamide and 2 g. hydroquinone. Hydrodimerization is eifected with 10.3 kg. potassium amalgam containing 14.42 g. potassium (0.140% potassium/ amalgam). A stoichiometrically equivalent quantity of glacial acetic acid is added at the same time as the amalgam so that the acid concentration is 10 meq./liter during the reaction. The experiment lasts minutes. The following results are obtained:

EXAMPLE 6 In this example, the acetic acid is replaced by sulfuric acid and various initial concentrations of acrylonitrile are used.

A solution containing various proportions (see table) of commercial acrylonitrile, formamide and 1% water is introduced into the reactor. A potassium amalgam containing 0.2% potassium is then passed through it. The temperature is kept at 20 C. and concentrated sulfuric acid is added at the same time as the amalgam so that the acid concentration is 10 meq./liter during the reaction. Potassium sulfate precipitates as soon as formed and is eliminated at the end of the reaction by filtration. The results obtained for the different acrylonitrile concentrations are shown in the following table:

TABLE 69. 6b 6c 6d Initial mixture:

Acrylonitrile (percent). 25 37.5 49 59 Formamide (percent) 74 61.5 50 40 Water (percent) 1 1 1 1 Potassium/acrylonitrile molar rat 0.87 0.68 0.64 0.57 Acrylonitrile conversion (percent). 88 73.7 67 52 Potassium conversion (percent) 100 87.4 65.0 Adiponitrile yield in relation to acrylonitrile (percent) 89.2 66.5 48.2 Adiponitrile yield in relation to potassium (percent) 90.5 96.8 81.0 83 Propionitrile yield in relation to acryl 'le (percent) 3 2.1 3.6 9.5 Propionitrile yield in relation to potassium (percent) 6.1 4.6 8.6 27 Adiponitrile/propionitrileweight ratio 28.8 41.3 18 5 Gaseous hydrogen produced (percent) 0 0 0 0 EXAMPLE 7 In this example, sodium amalgam is substituted for potassium amalgam and the acid is sulfuric acid.

A solution initially containing 40% commercial acrylonitrile, 55% formamide and 5% Water is introduced into the reactor." A sodium amalgam containing 0.12% sodium is passed through it in such an amount that the sodium/acrylonitrile molar ratio is 0.63 and concentrated sulfuric acid is added at the same time as the amalgam so that the concentration of the acid is maintained at 10 meq./liter. The temperature is kept at 20 C.

Acrylonitrile conversion, percent 61.9 Sodium conversion, percent 96.2 Adiponitrile yield in relation to acrylonitrile, percent 72.5 Adiponitrile yield in relation to sodium, percent 71.7 Propionitrile yield in relation to acrylonitrile, percent 5.9 Propionitrile yield in relation to sodium, percent 11.6 Adiponitrile/propionitrile weight ratio 12.1

Gaseous hydrogen produced 0 7 EXAMPLE 8 In this example, the amide is dimethylformamide.

A solution initially containing 10% commercial acrylonitrile, 80% dimethylformamide and 10% water is introduced into the reactor. A potassium amalgam containing 0.2% potassium is passed through it in such an amount that the potassium/acrylonitrile molar ratio is 1.23 and concentrated sulfuric acid is added at the same time as the amalgam so that the concentration of the acid is maintained at 1 to 2 meq./liter. The experiment is carried out at 20 C.

EXAMPLE 9 In this example, the amide is acetamide.

A solution initially containing 24.4% acrylonitrile, 59.5% acetamide and 16.6% water is introduced into the reactor. A potassium amalgam containing 0.2% potassium is then passed through it in such an amount that the potassium/acrylonitrile molar ratio is 0.66 and concentrated sulfuric acid is added at the same time as the amalgam so that the concentration of the acid is maintained at 3 to 5 meq./liter. The experiment is carried out at 20 C.

Acrylonitrile conversion, percent 62 Potassium conversion, percent 93 Adiponitrile yield in relation to acrylonitrile, percent 58.5 Adiponitrile yield in relation to potassium, percent 59.5 Propionitrile yield in relation to acrylonitrile, percent 13.8 Propionitrile yield in relation to potassium, percent 27.8 Adiponitrile/propionitrile weight ratio 4.2 Gaseous hydrogen produced 0 EXAMPLE In this example, the amide is p-toluene-sulfonamide mixed with dioxane.

A solution initially containing 23% acrylonitrile, 36.7% p-toluene-sulfonamide, 33.9% dioxane and 6.4% water is introduced into the reactor. A potassium amalgam containing 0.2% potassium is then passed through it in such an amount that the potassium/acrylonitrile molar ratio is 0.66 and concentrated sulfuric acid is added at the same time as the amalgam so that the concentration of the acid is maintained at 10 meq./liter. The experiment is carried out at 20 C.

Acrylonitrile conversion, percent 44.5 Potassium conversion, percent 100 Adiponitrile yield in relation to acrylonitrile, percent 40.9 Adiponitrile yield in relation to potassium, percent 27.6 Propionitrile yield in relation to acrylonitrile, percent 52.8 Propionitrile yield in relation to potassium, percent 71.5 Adiponitrile/propionitrile weight ratio 0.8

8 EXAMPLE 11 This example illustrates a continuous process.

A feed solution (constituted by 59% formamide, 40% acrylonitrile and 1% normal aqueous solution of sulfuric acid), the amalgam containing 0.2% potassium and the sulfuric acid meant to neutralize the consumed potassium are continuously introduced into the above described reactor. The exhausted mercury and the reaction suspension containing 10% potassium sulfate are continuously withdrawn. The suspension is filtered in a continuous manner and a determined portion of the filtrate is recycled with the above described reagents in such a way that a 10% concentration of potassium sulfate is maintained in the reactor and that the desired conversion of acrylonitrile is reached. The filtrate contains 57.5% formamide, 12.5% acrylonitrile, 25% adiponitrile, 0.7% propionitrile and 1% water, the balance being constituted by high boiling compounds. The acid concentration is automatically maintained at 10 meq./ liter by means of a pH-meter controlled valve. Temperature is kept at 1820 C.

Acrylonitrile conversion, percent 68.8 Potassium conversion, percent Adiponitrile yield in relation to acrylonitrile, percent 89.4 Adiponitrile yield in relation to potassium, percent 89 Propionitrile yield in relation to acrylonitrile, percent 2.5 Propionitrile yield in relation to potassium, percent" 5 Adiponitrile/propionitrile weight ratio 35.8

EXAMPLE 12 In this example, acrylonitrile is replaced by ethyl acrylate.

A solution initially containing 20% ethyl acrylate, 79% formamide and 1% water is introduced into the reactor. A potassium amalgam containing 0.2% potassium is then passed through it in such an amount that the potassium/ ethyl acrylate molar ratio is 0.945 and concentrated sulfuric acid is added at the same time as the amalgam so that the concentration of the acid is maintained at 10 meq./ liter. Temperature is kept at 20 C.

Percent Ethyl acrylate conversion 88 Potassium conversion 89.2 Diethyl adipate yield in relation to ethyl acrylate 80.6 Diethyl adipate yield in relation to potassium 75 Ethyl propionate yield: not detectable by gas chro matography.

EXAMPLE 13 Acrylo- Ethyl Potasmtrile acrylate sium Conversion, percent 55 65. 5 100 Adiponitrile yield, percent 22. 0 11.5 Diethyl adipate yield, percent 31 18. 5 Ethyl eyanopentanoate yield, percent- 57. 3 48. 1 57 Propionitrile yield, percent 6.7 6. 7 Ethyl propionate yield, percent 0 0 EXAMPLE 14 The example describes the hydrodimerization of an acrylonitrile-methacrylonitrile mixture.

A solution initially containing 59% formamide, 40% equimolecular mixture of acrylonitrile and methacrylonitrile and 1% water is introduced into the reactor. A potassium amalgam containing 0.2% of potassium is then passed through it in such an amount that the potassium/ total amount of two monomers molar ratio is 0.68 and concentrated sulfuric acid is added at the same time as the amalgam so that the concentration of the acid is maintained at 10 meq./liter. Temperature is kept at 20 C.

Aerylo- Methacry- Potasnitrile lonitrile sium Conversion, percent 98. 5 17 75 Adrponitrile yield, percent .4 69. 5 50 2,7-dimethyladiponitrile yield, percent Traces Traces 2-methyladiponitrile yield, percent- 11. 7 67. 16. 7 Propionitrile yield, percent Isobutyronitrile yield, percent 21. 2 5. 3

EXAMPLE 15 Methacrylonitrile conversion, percent 49.3 Dimethyladiponitrile yield in relation to methacrylonitrile, percent 49 Dimethyladiponitrile yield in relation to potassium,

percent H 29 Isobutyronitrile yield in relation to methacrylonitrile,

percent 58.5 Isobutyronitrile yield in relation to potassium, percent 70 Dimethyladiponitrile/isobutyronitrile weight ratio 0.82

EXAMPLE 16 This example is a variation of Example 15.

A solution initially containing 83% dimethylformamide, 15% methacrylonitrile and 2% water is introduced into the reactor. A potassium amalgam containing 0.2% potassium is then passed through it in such an amount that the consumed potassium/methacrylonitrile molar ratio is 0.3 and concentrated sulfuric acid is added at the same time as the amalgam so that the concentration of the acid is maintained below meq./liter. Temperature is kept at 40 C.

Methacrylonitrile conversion, percent 33 Dimethyladiponitrile yield in relation to methacrylonitrile, percent 33.5 Dimethyladiponitrile yield in relation to potassium,

percent 36.4 Isobutyronitrile yield in relation to methacrylonitrile,

percent 19.5 Isobutyronitrile yield in relation to potassium, percent 41.8 Dimethyladiponitrile/isobutyronitrile weight ratio 1.72

We claim:

1. A process for the reductive dimerization of acrylonitrile to produce adiponitrile which comprises contacting said acrylonitrile with an alkali metal amalgam and an acid in a liquid dimerization medium which contains therein hexamethylphosphoramide.

2. A process for the reductive dimerization of a compound selected from the group consisting of acrylonitrile, methacrylonitrile and ethyl acrylate to produce adiponitrile, dimethyl-adiponitrile and diethyl adipate respectively, which comprises contacting said compound with an alkali metal or alkaline earth metal amalgam and an acid in a liquid dimerization medium which contains therein hexamethylphosphoramide.

3. A process according to claim 2 wherein. acrylonitrile is contacted with an alkali metal or alkaline earth metal amalgam, the acid concentration in the reaction mixture is maintained between 0.1 and 100 milliequivalents of acid per liter of reaction mixture and the temperature of the reaction mixture is between 0 and 50 C. during dimerization.

4. A process according to claim 2, wherein said acid is selected from the group consisting of acetic acid, hydrochloric acid and sulfuric acid.

5. A process according to claim 2, wherein the concentration of said hexamethylphoshoramide in said liquid medium is between 10 and 95% by weight.

6. A process according to claim 2, wherein said liquid medium consists essentially of from 5 to by weight of acrylonitrile, from 20 to by weight of said amide and from 0 to 10%, inclusive, by weight of water.

References Cited UNITED STATES PATENTS 3,463,806 8/1969 Anderson et al. 2604658 A 3,489,789 1/1970 Dewar et al. 260-4658 FOREIGN PATENTS 1,436,896 3/1966 France 260-4658 JOSEPH P. BRUST, Primary Examiner U.S. Cl. X.R. 

